citrus是可数的还是不可数的?

The only way for growers to salvage frozen citrus is
to process them quickly into juice concentrate before
they rot when warmer weather returns.
(A) to process them quickly into juice concentrate
before they rot when warmer weather returns
(B) if they are quickly processed into juice
concentrate before warmer weather returns to
rot them
(C) for them to be processed quickly into juice
concentrate before the fruit rots when warmer
weather returns
(D) if the fruit is quickly processed into juice
concentrate before they rot when warmer
weather returns
(E) to have it quickly processed into juice
concentrate before warmer weather returns and
rots the fruit

OG的解释说citrus是单数的,因此要用单数代词it

如果citrus是单数的,为什么frozen citrus前面啥也没有?也没有a?

难道是不可数的?但是我查词典明明是可数的朗文说是countable.

谢谢指教.

就是句子里没有冠词,解释还说是单数让我矛盾了一把....